The sizing of glass fibers which are used to reinforce plastic resin matrices is well known. For instance, U.S. Pat. No. 3,997,306 discloses glass fiber size which contains a phenolic epoxy resin, the reaction product of the partial ester of a polycarboxylic acid containing one or more unesterified carboxyl groups with a compound containing more than one epoxy group, an amino silane coupling agent, a methacryloxy alkyl trialkoxy silane, and a non-ionic surface active agent.
U.S. Pat. No. 4,126,729 discloses gun roving glass fibers coated with an aqueous-based size comprising an epoxidized polyvinyl acetate copolymer in combination with a vinyl acetate-ethylene copolymer and a vinyl acetate copolymer.
U.S. Pat. No. 4,457,970 discloses treated glass fiber strands with improved processing characteristics. The treated glass fiber strands have on the glass fibers comprising the glass fiber strand an aqueous treating composition or a dried residue thereof. The treating composition has a vinyl-containing coupling agent, an epoxidized thermoplastic polymer or copolymer, an organo-reactable silane coupling agent in an unhydrolyzed and/or partially hydrolyzed condition or an interaction product of the epoxidized polymer or copolymer and organo-reactable silane coupling agent, and a glass fiber lubricant. U.S. Pat. No. 4,789,593 discloses glass fibers treated with an aqueous chemical treating composition having a polar thermoplastic film-forming polymer, coupling agent and lubricant. The aqueous emulsion of the thermoplastic film forming polymer has an average amount of aliphatic unsaturation of less than around 1.5 aliphatic double bonds/mole of polymer and has a ratio of aliphatic unsaturation to aromatic unsaturation not to exceed 0.1.
It is desirable to develop sizing compositions which provide better wettability of glass fibers by plastic resins than sizing compositions noted herein above. It is further desirable to develop sizing compositions which, when applied to glass fibers or strands which are used to reinforce plastic resin matrices, yield fiber-reinforced plastics (FRP) produced from the reinforced plastic resin matrices which have better clarity than laminates produced from polymeric matrices reinforced with glass fibers or strands treated with sizing compositions known heretofore.